Method of increasing cetane number of fuel oil



Dec. 4, 1945.

G. R. GILBERT ME THOD OF INCREASING CETANE NUMBER OF FUEL OIL Filed Dec. '7, 1942 Afro/MEX $5285 EE; m

fgwmvamolz. 1 BY M 9.530 nES Quuz M m2 Ewan Patented Dec. 4, 194! METHOD OF INCREASING CETANE NUMBER OF FUEL OIL George R. Gilbert, Elizabeth, N. J., assignor to Standard Oil Development Company, a corporation of Delaware Application December 7, 1942, Serial No. 468,119

2 Claims.

The present invention is directed to a method for improving the combustion characteristics of oils suitable for use in Diesel motors.

There has been a rapid increase in the use of Diesel engines and a corresponding demand for premium Diesel fuel oils of high octane number. Various means for increasing the cetane numbers of Diesel fuels are known to the prior art. These known processes usually involve solvent extraction, or doctor sweetening plus the addition of excess elementary sulfur or the employment of addition agents such as organic nitrates, or sulfur compounds. These known processes suffer the disadvantage that the sulfur content of the fuel is increased or else expensive chemicals are required.

It is an object of the present invention to provie a process for increasing the cetane number of fuel oils. More particularly, sour fuel stocks may be processed in accordance with the present invention to sweeten them and increase the cetane number Without increasing the sulfur content of these stocks and by the use of readily available treating materials.

It may be stated broadl that the present invention resides in contacting sour fuel oils in the presence of oxygen with hot caustic solution. Surprisingly enough it has been discovered that recycling the hot caustic results in a greater increase of the cetane number than is obtained when fresh caustic is employed.

The reason for the unexpectedly improved result obtained by employing hot caustic which has been previously contacted wth sour fuel oils is not clearly understood. It is known, however, that the presence of disulfides in a fuel oil increases the cetane number of the fuel. It is suggested that the contact of sour fuel with caustic and air converts the mercaptans to disulfides. However, the disulfides are somewhat soluble in caustic, as well as in the hydrocarbon fuel and some of the disulfides are dissolved in the new caustic while a remainder stays in the fuel to increase its cetane number. As the caustic is recirculated to contact succeeding amounts of fuel it dissolves disulfides progressivel less and less, since it is approaching saturation. Another theory is that phenols are known to have a low cetane number and are somewhat soluble in caustic. It may, therefore, be assumed that the removal of the phenols by the caustic and air causes the cetane number of the fuel to increase.

It is to be understood that I do not wish to be bound by either of the theories advanced above, and that irrespective of the chemical phenomeso drawn and used in non involved the treatment as described herein results in an unexpected improvement in the cetane number of the hydrocarbon fuel treated.

In practicing the present invention, the fuel oil to be treated may be heated to a temperature between and 210 F. and air added thereto either by exposing the mixture while being agitated to air to allow it to become saturated with air or by injecting a small amount of air into the oil in a closed system. The mixture may then be contacted with concentrated caustic solution, such as 50 Be. sodium hydroxide solution, for a short time. The used sodium hydroxide ma be recirculated through the system for a large :number of times before it becomes so spent that it must be discarded and as stated above the recirculated caustic gives a product of higher cetane number than does fresh caustic.

As a specific example 15 gallons of gas oil with an original copper number of were heated to a temperature of F. and contacted with one liter of hot 50 Be. sodium hydroxide with thorough mixing. The mixture was recirculated at the high temperature until it was substantially sweet and the mixture then allowed to settle.

The sodium hydroxide was withdrawn from the first batch and used to treat another 15 gallon charge of the sour gas oil with the mixture being recirculated until the second batch was practically sweet. The spent caustic was withlike manner for treating two more batches of the same original sour stock. The analytical data on the charge and each of the four batches treated by the process are given in the following table:

Charge Batchl Batch2 Batch3 Batch4 Getane number 47. l 49. 3 50. 0 50. 3 51. 4 Increase in cetanc number 0 2.2 2. 9 3. 2 4. 3 Odor S 0 ur Sweet Sweet Sweet Sweet Total sulfur content'..-.. 0. 82 0.75 0. 78 0. 77 O. 79

Whil in the above examples the charge stock was treated in batch operation, it will be apparcut that the process may be practiced commercially either by using batch operation or in a continuous operation. A continuous method for practicing the invention commercially will now be described in conjunction with the drawing in which the sole figure is a diagrammatical illustration of a preferred embodiment.

Sour fuel oil withdrawn from vessel 9 is heated in heating coil in to the desired temperature and mixed with hot recirculated caustic and air from line H in orifice plate mixer l2. The mixture is sent to separating vessel l3 provided with a coagulator bed I 4. In vessel I 3 caustic settles under the influence of gravity and is withdrawn via pipe line l5. To the recirculated caustic additional fresh caustic is added by line It and air by line H. The stream then flows through pump is to heater l9 where 'it is withdrawn by line H and admixed with sour oil as above described. If desired, a line provided with pump 2| may be used to bypass a portion of the emulsion withdrawn from mixture I2 before it is sent to separator l3 to obtain additional admixing of the components.

From the upper portion of separating vessel 13 line 22 removes air and oil. This admixture is sent to separator 23 where it is allowed to settle under the influence of gravity. Spent air is removed from vessel 23 by line 24 and separated oil removed from the bottom of separating vessel 23by line 25and admixed -with wash water added thereto byline 26. It will beunderstood that the separated "oil "contain suspended caustic and the water-is added to the oil for the purpose of removing this caustic. Th admixture of water 'ahdbil iss'ent through mixer '27 to a settling ves- "sel '28 'Wher'eit settles'underthe'influence of gravity with water discharging via line 29 and the finished fuel oil sent through line -30 to storage tank '-3'l a 'It will be evident that in continuous operation 'a'small amount of fresh caustic may be continuously added to the cycle and a small portion of spent caustic continuously withdrawn as shown in the drawing, or alternatively, fresh caustic and charge stock may be flowed concurrently mately 'Baum caustic solution and in the ratio of-approxirn'ately 15 parts of oil to 1 part of caustic in the presence of oxygen at a temperature of approximately F. until the batch is sweet, separating under the influence of gravity the oil from the caustic, admixing another batch of sour fuel oil with caustic, removed from said first batchyagitatingit in the presence "ofbxygen at a temperature of approximately 190 F. "until the oil is s'weet'a'nd's'eparating under the influence of gravity theoil from the caustic.

2. A method in accordance with claim 1 in which a plurality of batches'di sour oil-are serially treated with caustic separated batch.

from a preceding "GEORGE R.'G1LBERT. 

